Toll-like receptors (TLRs), a family of important innate immune molecules, are expressed both on the cell surface and in intracellular compartments of many immune and non-immune cells. TLRs are one of the best characterized innate pathogen recognition receptors (PRR). TLRs are transmembrane proteins which function as pattern recognition receptors for the detection and response to microbial ligands. To date, 10 TLRs have been identified in humans and 11 in mice. Natural or synthetic ligands for at least 9 TLRs have been identified. Activation of TLRs results in the recruitment of adaptor proteins including MyD88 (most TLRs except TLR3), TRIF (for TLR3 and TLR4), and Mal/TIRAP (TLR2 and TLR4) to the TIR domain. A series of phosphorylation/recruitment/activation events leads to the activation and translocation of the transcription factors nuclear factor-κB (NF-κB) NF-κB to the nucleus and the transcription of inflammatory and anti-inflammatory cytokine genes. While TLR induced innate immune responses help clear viral infections, TLRs have also been implicated in the immunopathology of virus infection. It is thought that TLR-mediated inflammatory response in response to viruses might contribute to diseases. In particular, it has been found that TLR2, TLR3, and TLR7 are involved in viral-associated immunopathology. Thus, in some circumstances, blockade of TLR-mediated signaling pathway may protect the host from the harmful inflammatory responses.
Although originally described as receptors for bacteria and fungi, it has now become clear that TLRs mediate the production of cytokines in response to a variety of viruses and viral ligands. A role for the Toll-like receptors, TLR2, TLR3, TLR4, TLR7 and TLR9, in the response to viruses has been established. Previous experiments have demonstrated that the cytokine response to human cytomegalovirus (CMV) and Herpes simplex virus-1 (HSV) is controlled by TLR2, while the response to respiratory syncytial virus (RSV) is dependent on TLR4 (13-15, 20). Previous studies have demonstrated that Lymphocytic choriomeningitis virus (LCMV) infection induces the activation of transcription factor nuclear factor-kappaB (NF-κB) and inflammatory responses through a TLR2/TLR6/CD14-MyD88/Mal-dependent signaling pathway. LCMV is the prototypic virus of the arenavirus family. Several members in the arenavirus family, including Lassa hemorrhagic fever (HF) virus and Argentine HF virus, cause severe, often lethal, viral hemorrhagic fevers in humans. Moreover, HF viruses have recently received considerable scrutiny because of the potential use of arenaviruses as biological weapons for bioterrorism (see the world wide web at bt.cdc.gov/agent/vhf).
Inhibiting TLR signaling in LCMV infected cells could have great therapeutic potential, not only in the treatment of LCMV disease (an arenavirus prototypic of the response to hemorrhagic fever viruses), but also in the treatment of other viral diseases involving TLR activation, including herpes encephalitis (HSV-1), genital herpes (HSV-2) and cytomegalovirus infection.
For example, ribavirin, a member of the nucleoside antimetabolite drugs that interfere with duplication of viral genetic material, is active against a number of DNA and RNA viruses, including hemorrhagic fever viruses; however, due to its side-effects, such as dose-dependent inhibiting effect on DNA synthesis, hemolytic anemia, and significant teratogenic effects, its application in clinical is limited. Accordingly, there is a need to develop new compounds that inhibit LCMV-induced NF-κB activation and cytokine responses through either modulating TLR2 expression or blocking LCMV replication. This invention addresses this need and others.